FIG. 1 is a schematic diagram of a conventional LC oscillator. The oscillator comprises a pair of N-type MOS transistors M1 and M2 that are cross-coupled by their drains and gates. The sources of transistors M1 and M2 are connected to a common bias current source Ib. The drain of each transistor M1 and M2 is connected to a high voltage supply node through a respective inductor La, Lb of same value. A capacitor C is connected between the drains of the transistors which form the differential outputs OPUT+ and OUT− of the oscillator. These output signals are in phase opposition. The output signals exhibit a low noise and a frequency that remains relatively accurate over a wide temperature range.
To provide more than two phases, for instance four phases in quadrature, it is known in the art to couple together two LC oscillators of the type shown in FIG. 1. Such a circuit is disclosed, for instance, in U.S. Pat. Nos. 6,456,167 and 7,436,266 (both incorporated herein by reference).
Thus, multiplying the number of low-noise oscillators to provide more phases is costly in terms of surface area, especially due to the inductors, and in terms of power consumption.